Method for allocating bearer identifier, apparatus, and system

ABSTRACT

Embodiments of this disclosure provide a session management method, an access management function device, and a session management device. The method carried out by an access and mobility management network element includes: obtaining subscription data of a terminal in a first communications network and subscription data of the terminal in a second communications network, where the subscription data of the terminal in the first communications network includes a DNN, and the subscription data of the terminal in the second communications network includes an APN corresponding to the DNN; allocating a bearer identifier to a bearer in a PDN connection corresponding to the APN; receiving a flow identifier that is of a flow in a PDU session corresponding to the DNN and that is sent by a session management network element; and sending the bearer identifier and the flow identifier to the terminal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2017/077371 filed on Mar. 20, 2017. The disclosure of theaforementioned application is hereby incorporated by reference in theentity.

TECHNICAL FIELD

Embodiments of this disclosure relate to the communications field, andmore specifically, to a method for allocating bearer identifier, anapparatus and a system.

BACKGROUND

With appearance of demands for networks such as the Internet of Thingsand the Internet of Vehicles, there are increasing requirements of userson a next generation mobile communications network, that is, a 5thgeneration (5G) mobile communications network. In the 5G network, toensure interworking between the 5G network and a 4G 4G) network orbetween the 5G network and another network (such as a 2G or 3G network),an interworking procedure similar to that between the 4G network and the3G network or between the 4G network and the 2G network is used. Forexample, handover is performed by using a solution of mobilitymanagement (MM) context mapping or session management (SM) contextmapping.

However, the solution in which handover is performed through contextmapping has a complex procedure, making it inconvenient to ensure adeployment process of the 5G network.

SUMMARY

Embodiments of this disclosure provide a session management method, tosimplify an interworking procedure between different communicationsnetworks.

According to a first aspect, a session management method is provided.The method includes: obtaining, by an access and mobility managementnetwork element, subscription data of a terminal in a firstcommunications network and subscription data of the terminal in a secondcommunications network, where the subscription data of the terminal inthe first communications network includes a DNN, and the subscriptiondata of the terminal in the second communications network includes anAPN corresponding to the DNN; allocating, by the access and mobilitymanagement network element, a bearer identifier to a bearer in a PDNconnection corresponding to the APN; receiving, by the access andmobility management network element, a flow identifier that is of a flowin a PDU session corresponding to the DNN and that is sent by a sessionmanagement network element; and sending, by the access and mobilitymanagement network element, the bearer identifier and the flowidentifier to the terminal.

In this embodiment, the access and mobility management network elementreserves a session resource for the second communications network, tosimplify an interworking procedure between different communicationsnetworks.

With reference to the first aspect, in a first possible implementationof the first aspect, the bearer in the PDN connection corresponding tothe APN is a default bearer, the flow in the PDU session correspondingto the DNN is a default flow, and before the allocating, by the accessand mobility management network element, a bearer identifier to a bearerin a PDN connection corresponding to the APN, the method furtherincludes: receiving, by the access and mobility management networkelement, a registration request message or a PDU session establishmentrequest message sent by the terminal; and after the receiving, by theaccess and mobility management network element, a registration requestmessage or a PDU session establishment request message, the methodfurther includes: sending, by the access and mobility management networkelement, the PDU session establishment request message to the sessionmanagement network element, where the PDU session establishment requestmessage includes a bearer identifier of the default bearer.

In this embodiment, the corresponding default bearer identifier isallocated to the default flow in a process of establishing the defaultflow in the PDU session, so that a session resource is reserved for thesecond communications network, thereby simplifying an interworkingprocedure between different communications networks.

With reference to the first aspect, in a second possible implementationof the first aspect, the bearer in the PDN connection corresponding tothe APN is a dedicated bearer, the flow in the PDU session correspondingto the DNN is a dedicated flow, and before the receiving, by the accessand mobility management network element, a flow identifier that is of aflow in a PDU session corresponding to the DNN and that is sent by asession management network element, the method further includes:receiving, by the access and mobility management network element, adedicated bearer identifier assignment request message sent by thesession management network element; and sending, by the access andmobility management network element, a dedicated bearer identifierassignment response message to the session management network element,where the dedicated bearer identifier assignment response messageincludes a bearer identifier of the dedicated bearer.

In this embodiment, the corresponding dedicated bearer identifier isallocated to the dedicated flow in a process of establishing thededicated flow in the PDU session, so that a session resource isreserved for the second communications network, thereby simplifying aninterworking procedure between different communications networks.

With reference to the first aspect, in a third possible implementationof the first aspect, the method further includes: receiving, by theaccess and mobility management network element, a handover request sentby an access network device; sending, by the access and mobilitymanagement network element, a session context request message to thesession management network element; receiving, by the access andmobility management network element, a session context response messagesent by the session management network element, where the sessioncontext response message includes the bearer identifier and a policy andcharging control rule of the default bearer in the PDN connection,and/or the bearer identifier and a policy and charging control rule ofthe dedicated bearer in the PDN connection; and sending, by the accessand mobility management network element, a relocation request to amobility management entity, where the location request includesindication information, and the indication information is used toinstruct the mobility management entity to reselect a serving gateway.

In this embodiment, to ensure handover of the terminal in differentnetworks, before the handover, the first communications network reservessession management resources for the second communications network, andduring the handover, the first communications network sends the sessionmanagement resources to the second communications network, and thesecond communications network can rapidly set up a service based on thesession management resources, thereby ensuring service continuity andsimplifying a handover procedure.

According to a second aspect, a session management method is provided.The method includes: obtaining, by a session management network element,a flow identifier of a flow in a PDU session corresponding to a DNN of aterminal, where the DNN is a DNN in subscription data of the terminal ina first communications network; obtaining, by the session managementnetwork element, a bearer identifier of a bearer in a PDN connectioncorresponding to an APN of the terminal, where the APN is an APN insubscription data of the terminal in a second communications network;and sending, by the session management network element, the beareridentifier and the flow identifier to an access and mobility managementnetwork element.

With reference to the second aspect, in a first possible implementationof the second aspect, the bearer in the PDN connection corresponding tothe APN is a default bearer, the flow in the PDU session correspondingto the DNN is a default flow, and the obtaining, by the sessionmanagement network element, a bearer identifier of a bearer in a PDNconnection corresponding to an APN of the terminal includes: receiving,by the session management network element, a PDU session establishmentrequest message sent by the access and mobility management networkelement, where the PDU session establishment request message includesthe bearer identifier.

With reference to the second aspect, in a second possible implementationof the second aspect, the bearer in the PDN connection corresponding tothe APN is a dedicated bearer, the flow in the PDU session correspondingto the DNN is a dedicated flow, and the obtaining, by the sessionmanagement network element, a bearer identifier of a bearer in a PDNconnection corresponding to an APN of the terminal includes: sending, bythe session management network element, a dedicated bearer identifierassignment request message to the access and mobility management networkelement; and receiving, by the session management network element, adedicated bearer identifier assignment response message sent by theaccess and mobility management network element, where the dedicatedbearer identifier assignment response message includes a beareridentifier of the dedicated bearer.

With reference to the second aspect, in a third possible implementationof the second aspect, the sending, by the session management networkelement, the bearer identifier and the flow identifier to an access andmobility management network element includes: sending, by the sessionmanagement network element, session management information to the accessand mobility management network element, where the session managementinformation includes an authorized QoS rule of the flow and anauthorized QoS rule of the bearer, the authorized QoS rule of the flowincludes the flow identifier, and the authorized QoS rule of the bearerincludes the bearer identifier.

With reference to the second aspect, in a fourth possible implementationof the second aspect, the obtaining, by a session management networkelement, a flow identifier of a flow in a PDU session corresponding to aDNN of a terminal includes: aggregating, by the session managementnetwork element according to a PCC rule of the terminal in the firstcommunications network, a service data flow corresponding to the PCCrule of the terminal in the first communications network to a dedicatedflow established for the terminal, where a flow identifier that is ofthe dedicated flow and that is obtained by the session managementnetwork element is a flow identifier of the dedicated flow establishedfor the terminal.

In this embodiment, the session management network element aggregates,according to the PCC rule of the terminal in the first communicationsnetwork, the service data flow corresponding to the PCC rule of theterminal in the first communications network to the dedicated flowestablished for the terminal, so that a correspondence between adedicated flow and a dedicated bearer can be established when a quantityof dedicated flows in a PDU session is greater than a quantity ofdedicated bearers in a PDN connection.

With reference to the second aspect, in a fifth possible implementationof the second aspect, the obtaining, by the session management networkelement, a bearer identifier of a bearer in a PDN connectioncorresponding to an APN of the terminal includes: aggregating, by thesession management network element according to a PCC rule of theterminal in the second communications network, a service data flowcorresponding to the PCC rule of the terminal in the secondcommunications network to a dedicated bearer established for theterminal, where the bearer identifier that is of the dedicated bearerand that is obtained by the session management network element is abearer identifier of the dedicated bearer established for the terminal.

According to a third aspect, a policy and charging control method isprovided. The method includes: obtaining, by a policy and chargingnetwork element, a service requirement of a terminal; and sending, bythe policy and charging network element, a packet data unit connectivityaccess network PDU-CAN session management message to a sessionmanagement network element, where the PDU-CAN session management messageincludes a policy and charging control PCC rule of the terminal in afirst communications network and a policy and charging control PCC ruleof the terminal in a second communications network.

With reference to the third aspect, in a first possible implementationof the third aspect, the policy and charging network element receives aPDU-CAN session establishment request message sent by the sessionmanagement network element, where the PDU-CAN session establishmentrequest message includes a subscription context corresponding to a DNNof the terminal in the first communications network and a PDNsubscription context corresponding to an APN of the terminal in thesecond communications network.

With reference to the third aspect, in a second possible implementationof the third aspect, the PCC rule of the terminal in the firstcommunications network and the PCC rule of the terminal in the secondcommunications network include: a quality of service class identifier ofthe terminal in the first communications network, an authorizedaggregate maximum bit rate Session-AMBR of a default flow in a PDUsession corresponding to the DNN, a quality of service class identifierof the terminal in the second communications network, and an authorizedAPN-AMBR of a default bearer in a PDN connection corresponding to theAPN.

With reference to the third aspect, in a third possible implementationof the third aspect, the obtaining, by a policy and charging networkelement, a service requirement of a terminal includes: receiving, by thepolicy and charging network element, the service requirement sent by theterminal or an application function network element, where the servicerequirement includes at least one of Internet Protocol IP filteringinformation, a media bandwidth requirement used for quality of serviceQoS control, and an application bandwidth requirement used for qualityof service QoS control.

With reference to the third aspect, in a fourth possible implementationof the third aspect, the PCC rule of the terminal in the firstcommunications network and the PCC rule of the terminal in the secondcommunications network include: a quality of service class identifier ofthe terminal in the first communications network, a quality of serviceclass identifier of the terminal in the second communications network,and at least one of the following: uplink and downlink packet filters, aguaranteed bit rate GBR, a maximum bit rate MBR, and an allocation andretention priority ARP.

With reference to the third aspect, in a fifth possible implementationof the third aspect, the service requirement further includes a servicecontinuity requirement.

According to a fourth aspect, an access and mobility management deviceis provided. The device includes: an obtaining unit, configured toobtain subscription data of a terminal in a first communications networkand subscription data of the terminal in a second communicationsnetwork, where the subscription data of the terminal in the firstcommunications network includes a DNN, and the subscription data of theterminal in the second communications network includes an APNcorresponding to the DNN; an allocation unit, configured to allocate abearer identifier to a bearer in a PDN connection corresponding to theAPN; a receiving unit, configured to receive a flow identifier that isof a flow in a PDU session corresponding to the DNN and that is sent bya session management network element; and a sending unit, configured tosend the bearer identifier and the flow identifier to the terminal.

According to a fifth aspect, a session management device is provided.The device includes: an obtaining unit, configured to: obtain a flowidentifier of a flow in a PDU session corresponding to a DNN of aterminal, and obtain a bearer identifier of a bearer in a PDN connectioncorresponding to an APN of the terminal, where the DNN is a DNN insubscription data of the terminal in a first communications network, andthe APN is an APN in subscription data of the terminal in a secondcommunications network; and a sending unit, configured to send thebearer identifier and the flow identifier to an access and mobilitymanagement network element.

According to a sixth aspect, a policy and charging control device isprovided. The device includes: an obtaining unit, configured to obtain aservice requirement of a terminal; and a sending unit, configured tosend a PDU-CAN session management message to a session managementnetwork element, where the PDU-CAN session management message includes apolicy and charging control PCC rule of the terminal in a firstcommunications network and a policy and charging control PCC rule of theterminal in a second communications network.

According to a seventh aspect, a computer program product is provided.The computer program product includes a computer program instruction.When the computer program instruction is executed on a computer, thecomputer performs the method according to any one of the first aspect tothe third aspect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an architecture applied to thetechnical solutions according to an embodiment of this disclosure;

FIG. 2 is a schematic flowchart of a session management method accordingto an embodiment of this disclosure;

FIG. 3 is another schematic flowchart of a session management methodaccording to an embodiment of this disclosure;

FIG. 4 is a schematic flowchart of a policy and charging control methodaccording to an embodiment of this disclosure;

FIG. 5 is still another schematic flowchart of a session managementmethod according to an embodiment of this disclosure;

FIG. 6 is yet another schematic flowchart of a session management methodaccording to an embodiment of this disclosure;

FIG. 7 is still yet another schematic flowchart of a session managementmethod according to an embodiment of this disclosure;

FIG. 8 is a further schematic flowchart of a session management methodaccording to an embodiment of this disclosure;

FIG. 9 is a schematic flowchart of a method for handing over UE betweencommunications networks according to an embodiment of this disclosure;

FIG. 10 is a schematic block diagram of an access and mobilitymanagement device according to an embodiment of this disclosure;

FIG. 11 is a schematic block diagram of a session management deviceaccording to an embodiment of this disclosure;

FIG. 12 is a schematic structural diagram of a policy and chargingcontrol device according to an embodiment of this disclosure; and

FIG. 13 is another schematic structural diagram of an access andmobility management device according to an embodiment of thisdisclosure.

DESCRIPTION OF EMBODIMENTS

A terminal in embodiments of this disclosure may include varioushandheld devices, in-vehicle devices, wearable devices, and computingdevices that have a radio communication function or another processingdevice connected to a wireless modem, and user equipment (UE), a mobilestation (MS), a terminal device, and the like that are in various forms.For ease of description, in this disclosure, an example in which theterminal is UE is used for description. The technical solutions in theembodiments of this disclosure are described below with reference to theaccompanying drawings.

FIG. 1 is a schematic diagram of a communications architecture appliedto the technical solutions according to an embodiment of thisdisclosure. In the communications architecture, UE accesses a corenetwork by using an evolved universal terrestrial radio access network(EUTRAN). Alternatively, the UE may access the core network by using anext generation radio access network (NG RAN) device. A device in thecore network includes a mobility management entity (MME), a servinggateway (SGW), a subscriber server, a policy and charging networkelement, a session management network element, a user-plane functionnetwork element, and an access and mobility management network element.Optionally, the access and mobility management network element may be anaccess and mobility management function (AMF). Optionally, in thisdisclosure, network elements may be connected by using interfaces shownin the accompanying drawings. For example, the MME and the AMF areconnected by using an Nx interface, and the SGW and the user-planefunction network element are connected by using an S5-U interface.

In this embodiment, the subscriber server is configured to storesubscription data of the UE. Optionally, the subscriber server mayinclude a home subscriber server (HSS) and unified data management(UDM). The HSS and the UDM are integrally deployed. A UDM function maybe added to the HSS, or an HSS function may be added to the UDM, or boththe HSS function and the UDM function are implemented in another device.In FIG. 1, the subscriber server is represented by using HSS+UDM.

The policy and charging network element includes a policy and chargingrules function (PCRF) and a policy control function (PCF). The PCRF andthe PCF are integrally deployed. The PCF function may be added to thePCRF, or the PCRF function may be added to the PCF, or both the PCRFfunction and the PCF function are implemented in another device. In FIG.1, the policy and charging network element is represented by usingPCRF+PCF.

The session management network element includes a session managementfunction (SMF) and a packet data network gateway-control plane (PGW-C).The SMF and the PGW-C are integrally deployed. A PGW-C function may beadded to the SMF, or the SMF function may be added to the PGW-C, or boththe SMF and the PGW-C function are implemented in another device. InFIG. 1, the session management network element is represented by usingSMF+PGW-C.

The user-plane function network element includes a user plane function(UPF) and a packet data network gateway-user plane (PGW-U). The UPF andthe PGW-U are integrally deployed. A PGW-U function may be added to theUPF, or the UPF function may be added to the PGW-U, or both the UPF andthe PGW-U function are implemented in another device. In FIG. 1, theuser-plane function network element is represented by using UPF+PGW-U.

The communications architecture shown in FIG. 1 includes a firstcommunications network and a second communications network. The firstcommunications network includes the AMF, the UDM, the PCF, the SMF, andthe UPF. Optionally, the first communications network may be a 5Gcommunications network. The second communications network includes theEUTRAN, the MME, the SGW, the HSS, the PCRF, the PGW-C, and PGW-U.Optionally, the second communications network may be a 4.5G or 4Gcommunications network. In the communications architecture shown in FIG.1, the UE may access the first communications network or may access thesecond communications network, and interworking of the UE between thefirst communications network and the second communications network maybe implemented.

FIG. 2 is a schematic flowchart of a session management method accordingto an embodiment of this disclosure. In this embodiment, the sessionmanagement method includes the following steps.

201. An access and mobility management network element obtainssubscription data of a terminal in a first communications network andsubscription data of the terminal in a second communications network,where the subscription data of the terminal in the first communicationsnetwork includes a data network name (DNN), and the subscription data ofthe terminal in the second communications network includes an accesspoint name (APN) corresponding to the DNN. Optionally, the access andmobility management network element is an AMF.

Optionally, the first communications network is a 5G communicationsnetwork. The second communications network may be a 4G communicationsnetwork.

Optionally, the subscription data of the terminal in the firstcommunications network further includes a subscription contextcorresponding to the DNN, and the subscription data of the terminal inthe second communications network further includes a packet data network(PDN) subscription context corresponding to the APN.

Optionally, the DNN includes a default DNN, the APN includes a defaultAPN, and the default DNN corresponds to the default APN. Optionally, theDNN includes a non-default DNN, the APN includes a non-default APN, andthe non-default DNN corresponds to the non-default APN.

Optionally, that an access and mobility management network elementobtains subscription data of a terminal in a first communicationsnetwork and subscription data of the terminal in a second communicationsnetwork includes: The access and mobility management network elementsends a location update request message to a subscriber server; and theaccess and mobility management network element receives a locationupdate response message sent by the subscriber server, where thelocation update response message includes the subscription data of theterminal in the first communications network and the subscription dataof the terminal in the second communications network. Optionally, thesubscriber server is a UDM.

Optionally, that the access and mobility management network elementsends a location update request to a subscriber server includes: Theaccess and mobility management network element sends a first locationupdate request to the UDM, and the access and mobility managementnetwork element sends a second location update request to the UDM; andthat the access and mobility management network element receives alocation update response sent by the subscriber server, where thelocation update response includes the subscription data of the terminalin the first communications network and the subscription data of theterminal in the second communications network includes: The access andmobility management network element receives a first location updateresponse sent by the UDM, where the first location update responseincludes the subscription data of the terminal in the firstcommunications network; and the access and mobility management networkelement receives a second location update response sent by the UDM,where the second location update response includes the subscription datain the second communications network.

202. The access and mobility management network element allocates abearer identifier to a bearer (Default bearer) in a PDN connectioncorresponding to the APN.

Optionally, a bearer identifier of a default bearer corresponds to aflow identifier of a default flow. For example, the bearer identifier ofthe default bearer is in a one-to-one correspondence with the flowidentifier of the default flow.

Optionally, a bearer identifier of a dedicated bearer corresponds to aflow identifier of a dedicated flow. For example, the bearer identifierof the dedicated bearer is in a one-to-one correspondence with the flowidentifier of the dedicated flow, or the bearer identifier of thededicated bearer corresponds to a flow identifier of a flow obtainedafter a plurality of dedicated flows are aggregated, or a beareridentifier of a bearer obtained after a plurality of dedicated bearersare aggregated corresponds to a flow identifier of a dedicated flow.

Optionally, the bearer in the PDN connection corresponding to the APN isa default bearer, and a flow in a PDU session corresponding to the DNNis a default flow. Before the access and mobility management networkelement allocates the bearer identifier to the bearer in the PDNconnection corresponding to the APN, the method further includes: Theaccess and mobility management network element receives a registrationrequest message or a PDU session establishment request message sent bythe terminal. After the access and mobility management network elementreceives the registration request message or the PDU sessionestablishment request message, the method further includes: The accessand mobility management network element sends the PDU sessionestablishment request message to a session management network element,where the PDU session establishment request message includes a beareridentifier of the default bearer. Optionally, the session managementnetwork element is an SMF.

Optionally, the registration request message or the PDU sessionestablishment request message further includes indication information.The indication information is used to indicate to the access andmobility management network element that the terminal has a capabilityto perform communication in the first communications network and thesecond communications network, and/or is used to indicate to the accessand mobility management network element that the terminal has asingle-registration or dual-registration capability.

Optionally, the bearer in the PDN connection corresponding to the APN isa dedicated bearer, and a flow in a PDU session corresponding to the DNNis a dedicated flow. Before the access and mobility management networkelement receives a flow identifier that is of the flow in the PDUsession corresponding to the DNN and that is sent by a sessionmanagement network element, the method further includes: The access andmobility management network element receives a dedicated beareridentifier assignment request message sent by the session managementnetwork element, and the access and mobility management network elementsends a dedicated bearer identifier assignment response message to thesession management network element, where the dedicated beareridentifier assignment response message includes a bearer identifier ofthe dedicated bearer.

Optionally, the PDU session establishment request message sent by theaccess and mobility management network element to the session managementnetwork element further includes the subscription context correspondingto the DNN and the PDN subscription context corresponding to the APN.Optionally, the PDU session establishment request message furtherincludes indication information. The indication information is used toindicate to the session management network element that the terminal hasa capability to perform communication in the first communicationsnetwork and the second communications network, and/or is used toindicate to the session management network element that the terminal hasa single-registration capability.

203. The access and mobility management network element receives a flowidentifier (flow ID) that is of a flow in a PDU session corresponding tothe DNN and that is sent by a session management network element.

Optionally, before the access and mobility management network elementreceives a session management message sent by the session managementnetwork element, the access and mobility management network elementdetermines that the terminal has the capability to perform communicationin the first communications network and the second communicationsnetwork and that an interface exists between the access and mobilitymanagement network element and a mobility management entity, and/or thatthe terminal has the single-registration capability.

Optionally, before the access and mobility management network elementreceives the session management message sent by the session managementnetwork element, the access and mobility management network elementselects the session management network element based on a fact that theterminal has the capability to perform communication in the firstcommunications network and the second communications network and thatthe interface exists between the access and mobility management networkelement and the mobility management entity, and/or that the terminal hasthe single-registration capability.

Optionally, the access and mobility management network element receivesthe session management information sent by the session managementnetwork element, and the session management information includes anauthorized quality of service (QoS) rule of the flow and an authorizedQoS rule of the bearer. The authorized QoS rule of the flow includes theflow identifier, and the authorized QoS rule of the bearer includes thebearer identifier.

Optionally, the session management information includes the flowidentifier of the default flow, an authorized session aggregate maximumbit rate (Session-AMBR) of the default flow, the bearer identifier ofthe default bearer, and an authorized APN-AMBR of the default bearer.

Optionally, the session management information includes a flowidentifier of a guaranteed bit rate (Guaranteed Bit Rate, GBR) flow, anuplink packet filter of the GBR flow, a bearer identifier of a GBRdedicated bearer, and a traffic flow template (TFT) of the GBR dedicatedbearer. Optionally, content included in the uplink packet filter is thesame as content included in the uplink traffic flow template herein.

204. The access and mobility management network element sends the beareridentifier and the flow identifier to the terminal.

Optionally, the access and mobility management network element sends thesession management information to the terminal. The session managementinformation includes the bearer identifier and the flow identifier.

Optionally, the method in this embodiment further includes: The accessand mobility management network element receives a handover request sentby an access network device; the access and mobility management networkelement sends a session context request message to the sessionmanagement network element; the access and mobility management networkelement receives a session context response message sent by the sessionmanagement network element, where the session context response messageincludes the bearer identifier and a policy and charging control (PCC)rule of the default bearer in the PDN connection; and/or the beareridentifier and a PCC rule of the dedicated bearer in the PDN connection;and the access and mobility management network element sends arelocation request to the mobility management entity, where therelocation request includes indication information, and the indicationinformation is used to instruct the mobility management entity toreselect a serving gateway. Optionally, address information of theserving gateway may be set to 0.0.0.0, to instruct the mobilitymanagement entity to reselect the serving gateway.

FIG. 3 is another schematic flowchart of a session management methodaccording to an embodiment of this disclosure. In this embodiment, forcontent similar to that in the embodiment of FIG. 2, refer todescriptions corresponding to the embodiment of FIG. 2, and details arenot described herein again. The session management method includes thefollowing steps.

301. A session management network element obtains a flow identifier of aflow in a PDU session corresponding to a DNN of a terminal, where theDNN is a DNN in subscription data of the terminal in a firstcommunications network.

Optionally, the session management network element allocates the flowidentifier to the flow in the PDU session corresponding to the DNN ofthe terminal.

Optionally, the session management network element aggregates, accordingto a PCC rule of the terminal in the first communications network, aservice data flow corresponding to the PCC rule of the terminal in thefirst communications network to a dedicated flow established for theterminal, and a flow identifier that is of a dedicated flow and that isobtained by the session management network element is a flow identifierof the dedicated flow established for the terminal.

302. The session management network element obtains a bearer identifierof a bearer in a packet data network PDN connection corresponding to anaccess point name APN of the terminal, where the APN is an APN insubscription data of the terminal in a second communications network.

The subscription data of the terminal in the first communicationsnetwork further includes a subscription context corresponding to theDNN, and the subscription data of the terminal in the secondcommunications network further includes a PDN subscription contextcorresponding to the APN. Optionally, a PDU session establishmentrequest message received by the session management network elementfurther includes the subscription context corresponding to the DNN andthe PDN subscription context corresponding to the APN. Optionally, thePDU session establishment request message further includes indicationinformation. The indication information is used to indicate to thesession management network element that the terminal has a capability toperform communication in the first communications network and the secondcommunications network, and/or is used to indicate to the sessionmanagement network element that the terminal has a single-registrationcapability.

Optionally, the bearer in the PDN connection corresponding to the APN isa default bearer, and the flow in the PDU session corresponding to theDNN is a default flow. That the session management network elementobtains a bearer identifier of a bearer in a PDN connectioncorresponding to an APN of the terminal includes: The session managementnetwork element receives the PDU session establishment request messagesent by an access and mobility management network element, where the PDUsession establishment request message includes the bearer identifier.

Optionally, the session management network element aggregates, accordingto a PCC rule of the terminal in the second communications network, aservice data flow corresponding to the PCC rule of the terminal in thesecond communications network to a dedicated bearer established for theterminal, and a bearer identifier that is of a dedicated bearer and thatis obtained by the session management network element is a beareridentifier of the dedicated bearer established for the terminal.

Optionally, the bearer in the PDN connection corresponding to the APN isa dedicated bearer, and the flow in the PDU session corresponding to theDNN is a dedicated flow. That the session management network elementobtains a bearer identifier of a bearer in a packet data network PDNconnection corresponding to an APN of the terminal includes: The sessionmanagement network element sends a dedicated bearer identifierassignment request message to the access and mobility managementnetwork, and the session management network element receives a dedicatedbearer identifier assignment response message sent by the access andmobility management network element, where the dedicated beareridentifier assignment response message carries a bearer identifier ofthe dedicated bearer.

303. The session management network element sends the bearer identifierand the flow identifier to an access and mobility management networkelement.

Optionally, that the session management network element sends the beareridentifier and the flow identifier to an access and mobility managementnetwork element includes: The session management network element sendssession management information to the access and mobility managementnetwork element, where the session management information includes anauthorized quality of service QoS rule of the flow and an authorized QoSrule of the bearer, the authorized QoS rule of the flow includes theflow identifier, and the authorized QoS rule of the bearer includes thebearer identifier.

Optionally, the session management information includes a flowidentifier of the default flow, an authorized Session-AMBR of thedefault flow, a bearer identifier of the default bearer, and anauthorized APN-AMBR of the default bearer.

Optionally, the session management information includes a flowidentifier of a GBR flow, an uplink packet filter (UL Packet filter) ofthe GBR flow, a bearer identifier of a GBR dedicated bearer, and anuplink traffic flow template (TFT) of the GBR dedicated bearer.Optionally, content included in the uplink packet filter is the same ascontent included in the uplink traffic flow template herein.

Optionally, the method in this embodiment may further include: Thesession management network element sends a PDU connectivity accessnetwork (P PDU-CAN) session establishment request message to a policyand charging network element, where the PDU-CAN session establishmentrequest message includes the subscription context corresponding to theDNN and the PDN subscription context corresponding to the APN; and thesession management network element receives a PDU-CAN sessionestablishment response message sent by the policy and charging networkelement, where the PDU-CAN session establishment response messageincludes a policy and charging control PCC rule of the terminal in thefirst communications network and a policy and charging control PCC ruleof the terminal in the second communications network. Optionally, thePDU-CAN session establishment request message further includesindication information. The indication information is used to indicateto the policy and charging network element that the terminal has thecapability to perform communication in the first communications networkand the second communications network, and/or is used to indicate to thepolicy and charging network element that the terminal has thesingle-registration capability.

Optionally, the PCC rules include a quality of service class identifier(QCI) of the terminal in the first communications network, a QCI of theterminal in the second communications network, and at least one of thefollowing: uplink and downlink packet filters (UL+DL Packet filters), aguaranteed bit rate (GBR), a maximum bit rate (MBR), and an allocationand retention priority (ARP).

Optionally, the method in this embodiment may further include: Thesession management network element receives a PDU-CAN sessionmodification request message sent by a policy and charging networkelement, where the PDU-CAN session modification response messageincludes the policy and charging control PCC rule of the terminal in thefirst communications network and the policy and charging control PCCrule of the terminal in the second communications network. Optionally,the policy and charging network element is a PCF.

FIG. 4 is a schematic flowchart of a policy and charging control methodaccording to an embodiment of this disclosure. In this embodiment, forcontent similar to that in the embodiments of FIG. 2 and FIG. 3, referto descriptions corresponding to the embodiments of FIG. 2 and FIG. 3,and details are not described herein again. The policy and chargingcontrol method includes the following steps.

401. A policy and charging network element obtains a service requirementof a terminal.

Optionally, that a policy and charging network element obtains a servicerequirement of a terminal includes: The policy and charging networkelement receives a PDU-CAN session establishment request message sent bya session management network element, where the PDU-CAN sessionestablishment request message includes a subscription contextcorresponding to a data network name DNN of the terminal in a firstcommunications network and a packet data network PDN subscriptioncontext corresponding to an access point name APN of the terminal in asecond communications network. Optionally, the PDU-CAN sessionestablishment request message further includes indication information.The indication information is used to indicate to the policy andcharging network element that the terminal has a capability to performcommunication in the first communications network and the secondcommunications network, and/or is used to indicate to the policy andcharging network element that the terminal has a single-registrationcapability.

Optionally, that a policy and charging network element obtains a servicerequirement of a terminal includes: The policy and charging networkelement receives the service requirement sent by the terminal or anapplication function network element, where the service requirementincludes at least one of Internet Protocol IP filtering information, amedia bandwidth requirement used for QoS control, and an applicationbandwidth requirement used for QoS control. Optionally, the applicationfunction network element is an application function (AF). Optionally,the policy and charging network element receives a PDU-CAN sessionmodification request from the session management network element orreceives a service notification message from the application function.The policy and charging network element receives the PDU-CAN sessionmodification request from the session management network element in adedicated flow establishment process initiated by UE, and the policy andcharging network element receives the service notification message fromthe application function in a dedicated flow establishment processinitiated by the AF. The PDU-CAN session modification request or theservice notification message includes the service requirement of theterminal. Optionally, the service requirement further includes a servicecontinuity requirement.

402. The policy and charging network element sends a PDU-CAN sessionmanagement message to a session management network element, where thePDU-CAN session management message includes a policy and chargingcontrol PCC rule of the terminal in a first communications network and apolicy and charging control PCC rule of the terminal in a secondcommunications network.

Optionally, the PDU-CAN session management message is a PDU-CAN sessionestablishment response message. The PCC rule of the terminal in thefirst communications network and the PCC rule of the terminal in thesecond communications network include: a QCI of the terminal in thefirst communications network, an authorized Session-AMBR of a defaultflow in a PDU session corresponding to the DNN, a QCI of the terminal inthe second communications network, and an authorized APN-AMBR of adefault bearer in a PDN connection corresponding to the APN.

Optionally, the PDU-CAN session management message is a PDU-CAN sessionmodification response message or a PDU-CAN session modification requestmessage. In the dedicated flow establishment process initiated by theUE, the PDU-CAN session management message is the PDU-CAN sessionmodification response message. In the dedicated flow establishmentprocess initiated by the AF, the PDU-CAN session management message isthe PDU-CAN session modification request message. The PCC rule of theterminal in the first communications network and the PCC rule of theterminal in the second communications network include: a QCI of theterminal in the first communications network, a QCI of the terminal inthe second communications network, and at least one of the following:uplink and downlink packet filters (UL+DL Packet filters), a GBR, anMBR, and an ARP.

The embodiments of this disclosure are described below by using anexample in which the first communications network is a 5G communicationsnetwork and the second communications network is a 4G network. Toclearly and briefly describe the embodiments of this disclosure, onlystep procedures and network elements that are related to this disclosureare shown in the embodiments of this disclosure. Others are technicalcontent well known to a person skilled in the art, and are not shown inthe accompanying drawings. For example, an access network device that isconfigured to receive information from UE or send information to UE byusing an air interface is not shown in the accompanying drawings.

In accompanying drawings of FIG. 5 to FIG. 9, for clear and briefdescriptions, an SMF, a PCF, a UPF, and UDM are separately used torepresent corresponding core network devices that are integrallydeployed in the 5G network and the 4G network.

FIG. 5 is still another schematic flowchart of a session managementmethod according to an embodiment of this disclosure. In thisembodiment, for content similar to that in the embodiments of FIG. 2 toFIG. 4, refer to descriptions corresponding to the embodiments of FIG. 2to FIG. 4, and details are not described herein again. Specifically,FIG. 5 shows a session management method in a UE registration process.The session management method in this embodiment includes the followingsteps.

501. UE sends a registration request to an AMF.

Optionally, the registration request may include indication information.The indication information is used to indicate that the UE has acapability to perform communication in a 5G network and a 4G network,and/or is used to indicate to the AMF that the UE has asingle-registration or dual-registration capability.

502. The UE and a network side device complete an authentication andsecurity procedure.

503. The AMF sends a location update request message to UDM.

Optionally, when an HSS and the UDM are integrally deployed, the AMFsends the location update request message to the UDM. The locationupdate request message includes indication information. The indicationinformation is used to indicate that the UE has the capability toperform communication in the 5G network and the 4G network. Optionally,the indication information may be interworking indication information.

Optionally, when an HSS and the UDM are integrally deployed, the AMFsends a first location update request and a second location updaterequest message to the UDM. Optionally, if the AMF changes compared withprevious registration or the AMF does not have an authorizedsubscription context for the current UE or the AMF does not have anauthorized context corresponding to an SUPI provided by the UE, the AMFmay initiate a location update procedure.

504. The AMF receives a location update response message sent by theUDM.

The location update response message includes subscription data of theUE in the 5G network and subscription data of the UE in the 4G network.The subscription data in the 5G network includes a DNN, and thesubscription data in the 4G network includes an APN.

Optionally, the DNN includes a default DNN, and the APN includes adefault APN. Optionally, the DNN includes a non-default DNN, and the APNincludes a non-default APN. Optionally, the subscription data in the 5Gnetwork may include only one default DNN. The subscription data in the5G network may further include one or more non-default DNNs. Thesubscription data in the 4G network may include only one default APN.The subscription data in the 4G network may further include one or morenon-default APNs, for example, an IP multimedia subsystem (IMS) APN or anon-3rd Generation Partnership Project (3GPP) APN.

Optionally, the default DNN is in a one-to-one correspondence with thedefault APN, and the non-default DNN is in a one-to-one correspondencewith the non-default APN. Alternatively, the non-default DNN may not bein a one-to-one correspondence with the non-default APN, for example, aquantity of non-default DNNs is greater than a quantity of non-defaultAPNs.

Optionally, a session corresponding to the DNN may include only onedefault flow. A PDU session corresponding to the DNN may further includeone or more dedicated flows. A PDN connection corresponding to the APNmay include only one default bearer. A PDN connection corresponding tothe DNN may further include one or more dedicated bearers.

Optionally, the subscription data of the UE in the 5G network furtherincludes a subscription context corresponding to the DNN. Thesubscription data of the UE in the 4G network further includes a PDNsubscription context corresponding to the APN. Optionally, the PDNsubscription context includes a QoS parameter such as a subscriptionAPN-AMBR and/or a subscription QoS profile.

Optionally, the location update response received by the AMF includes acorrespondence between the DNN and the APN. For example, thecorrespondence between the DNN and the APN may be represented by using alist, or the correspondence may be represented by using a locationrelationship between the DNN and the APN in the message, and details arenot described herein again.

Optionally, after receiving the location update response, the AMF mayobtain the correspondence between the DNN and the APN based on a domainname in the subscription data of the UE in the 5G network and a domainname in the subscription data of the UE in the 4G network. For example,the PDN subscription context includes 4g.ims.org, and the subscriptioncontext corresponding to the DNN includes 5g.ims.org, so that the AMFobtains the correspondence between the DNN and the APN based on a factthat the domain names each include ims.org.

Optionally, when the HSS and the UDM are integrally deployed, the AMFreceives the location update response sent by the UDM. The locationupdate response includes the subscription data of the UE in the 5Gnetwork and the subscription data of the UE in the 4G network.

Optionally, when the HSS and the UDM are integrally deployed, the AMFreceives a first location update response and a second location updateresponse that are sent by the UDM. The first location update responseincludes the subscription data of the UE in the 5G network, and thesecond location update response includes the subscription data of the UEin the 4G network.

505. The AMF allocates a bearer identifier (bearer ID) to a defaultbearer in a PDN connection corresponding to an APN.

506. The AMF sends a PDU session establishment request message to anSMF, where the PDU session establishment request message includes thebearer identifier that is of the default bearer and that is allocated bythe AMF.

Optionally, the PDU session establishment request message may furtherinclude indication information. The indication information is used toindicate that the UE has the capability to perform communication in the5G network and the 4G network, and/or is used to indicate to the SMFthat the UE has the single-registration capability.

Optionally, the PDU session establishment request message may furtherinclude the PDN subscription context corresponding to the APN and thesubscription context corresponding to the DNN.

Optionally, before sending the PDU session establishment request messageto the SMF, the AMF may select the SMF based on a fact that the UE hasthe capability to perform communication in the 5G network and the 4Gnetwork and that a communications interface exists between the AMF andan MME, and/or that the UE has the single-registration capability.

507. The SMF allocates a flow identifier to a default flow in a PDUsession corresponding to a DNN.

Optionally, the flow identifier that is of the default flow and that isallocated by the SMF is in a one-to-one correspondence with the beareridentifier that is of the default bearer and that is allocated by theAMF.

508. The SMF obtains a PCC rule of the UE in a 5G network and a PCC ruleof the UE in a 4G network by using a PDU-CAN session establishmentprocedure.

Optionally, the PCC rules include a QCI of the UE in the 5G network, anauthorized AMBR of the PDU session corresponding to the DNN, a QCI ofthe UE in the 4G network, an authorized AMBR of the PDN connectioncorresponding to the APN, and an ARP.

Optionally, the SMF sends the PDU-CAN session establishment requestmessage to a PCF. The PDU-CAN session establishment request messageincludes the subscription context corresponding to the DNN and the PDNsubscription context corresponding to the APN, and may further includeindication information. The indication information is used to indicatethat the UE has the capability to perform communication in the 5Gnetwork and the 4G network, and/or is used to indicate to the PCF thatthe UE has the single-registration capability. The SMF receives aPDU-CAN session establishment response message sent by the PCF. ThePDU-CAN session establishment response message includes the PCC rule ofthe UE in the 5G network and the PCC rule of the UE in the 4G network.

In this embodiment, step 507 may be performed before step 508, or step508 may be performed before step 507. This is not limited herein.

509. The SMF sends a PDU session establishment response message to theAMF, where the PDU session establishment response message includes theflow identifier that is of the default flow in the PDU sessioncorresponding to the DNN and that is allocated by the SMF.

Optionally, the PDU session establishment response message may furtherinclude the bearer identifier allocated by the AMF to the default bearerin the PDN connection corresponding to the APN.

Optionally, the PDU session establishment response message may furtherinclude session management information. The session managementinformation includes an authorized QoS rule of the default flow in thePDU session and an authorized QoS rule of the default bearer in the PDNconnection. Optionally, the authorized QoS rule of the default flow inthe PDU session includes the flow identifier of the default flow, andthe authorized QoS rule of the default bearer in the PDN connectionincludes the bearer identifier of the default bearer.

Optionally, the authorized QoS rule of the default flow in the PDUsession may further include the authorized AMBR of the PDU session. Theauthorized QoS rule of the default bearer in the PDN connection includesthe authorized AMBR of the PDN connection.

510. The AMF sends a registration accept message to the UE, where theregistration accept message includes the flow identifier that is of thedefault flow and that is allocated by the SMF and the bearer identifierthat is of the default bearer and that is allocated by the AMF.

Optionally, the registration accept message may further include theauthorized QoS rule of the default flow in the PDU session and theauthorized QoS rule of the default bearer in the PDN connection.

Optionally, the registration accept message includes the sessionmanagement information included in the PDU session establishmentresponse message.

In this embodiment, in a UE registration process, the AMF obtains thesubscription data of the UE in the 5G network and the subscription dataof the UE in the 4G network in advance, and the AMF allocates thecorresponding default bearer in the 4G network to the default flow inthe session in a PDU session establishment process in the 5G network,thereby avoiding a case in which a correspondence between the defaultflow in the PDU session in the 5G network and the default bearer in thePDN connection in the 4G network is established by using a mappingmethod. According to the method in this embodiment, interworking of theUE in different networks is simpler. For example, when the UE is handedover from the 5G network to the 4G network, a procedure is simpler.

FIG. 6 is yet another schematic flowchart of a session management methodaccording to an embodiment of this disclosure. In this embodiment, forcontent similar to that in the embodiments of FIG. 2 to FIG. 5, refer todescriptions corresponding to the embodiments of FIG. 2 to FIG. 5, anddetails are not described herein again. Specifically, FIG. 6 shows asession management method in a procedure in which UE actively initiatesa PDU session. The session management method in this embodiment includesthe following steps.

601. UE sends a PDU session establishment request message to an AMF.

Optionally, the PDU session establishment request message may includeindication information. The indication information is used to indicatethat the UE has a capability to perform communication in a 5G networkand a 4G network, and/or is used to indicate to an SMF that the UE has asingle-registration or dual-registration capability.

602. The AMF allocates a bearer identifier to a default bearer in a PDNconnection corresponding to an APN.

603. The AMF sends the PDU session establishment request message to anSMF.

Content in this step is similar to that in step 506, and details are notdescribed herein again.

604. The SMF allocates a flow identifier to a default flow in a PDUsession corresponding to a DNN.

Content in this step is similar to that in step 507, and details are notdescribed herein again.

605. The SMF obtains a PCC rule of the UE in a 5G network and a PCC ruleof the UE in a 4G network by using a PDU-CAN session establishmentprocedure.

Content in this step is similar to that in step 508, and details are notdescribed herein again.

606. The SMF sends a session establishment request message to a UPF.

Optionally, the session establishment request message includesindication information. The indication information is used to indicatethat the UE has the capability to perform communication in the 5Gnetwork and the 4G network.

Optionally, when the UPF and a PGW-U are integrally deployed, thesession establishment request message may be an N4 session establishmentrequest message. When the UPF and the PGW-U are separately deployed, theSMF sends the N4 session establishment request message to the UPF, andthe SMF sends an Sxb session establishment request message to the PGW-U.

607. The SMF receives a session establishment response message sent bythe UPF, where the session establishment response message includes atunnel ID of the UPF and a tunnel ID of a PGW-U.

Optionally, when the UPF and the PGW-U are separately deployed, the SMFreceives, by using an N4 interface, the session establishment responsemessage sent by the UPF, and the session establishment response messageincludes the tunnel ID of the UPF. The SMF receives, by using an Sxbinterface, a session establishment response message sent by the PGW-U,and the session establishment response message includes the tunnel ID ofthe PGW-U.

The SMF establishes a data transmission channel to the UPF by using step606 and step 607.

608. The SMF sends a PDU session establishment response message to theAMF.

Content in this step is similar to that in step 509, and details are notdescribed herein again.

609. The AMF sends a PDU session establishment accept message to the UE,where the PDU session establishment accept message includes the flowidentifier that is of the default flow and that is allocated by the SMFand the bearer identifier that is of the default bearer and that isallocated by the AMF.

Optionally, the PDU session establishment accept message may furtherinclude an authorized QoS rule of the default flow in the PDU sessionand an authorized QoS rule of the default bearer in the PDN connection.

Optionally, the PDU session establishment accept message includessession management information included in the PDU session establishmentresponse message in step 608.

610. The AMF receives a PDU session establishment acknowledgement (ACK)message sent by the UE.

In this embodiment, in a PDU session establishment process initiated bythe UE, the AMF allocates the corresponding default bearer in the 4Gnetwork to the default flow in the session, thereby avoiding a case inwhich a correspondence between the default flow in the PDU session inthe 5G network and the default bearer in the PDN connection in the 4Gnetwork is established by using a mapping method. According to themethod in this embodiment, interworking of the UE in different networksis simpler. For example, when the UE is handed over from the 5G networkto the 4G network, a procedure is simpler.

FIG. 7 is still yet another schematic flowchart of a session managementmethod according to an embodiment of this disclosure. In thisembodiment, for content similar to that in the embodiments of FIG. 2 toFIG. 6, refer to descriptions corresponding to the embodiments of FIG. 2to FIG. 6, and details are not described herein again. Specifically,FIG. 7 shows a procedure in which UE initiates establishment of adedicated flow in a PDU session. A session management method in thisembodiment includes the following steps.

701. UE sends a PDU session modification request message to an AMF.

Optionally, the PDU session modification request message includes aservice requirement of the UE. The service requirement includes at leastone of Internet Protocol (IP) filtering information, a media bandwidthrequirement used for QoS control, and an application bandwidthrequirement used for QoS control.

Optionally, the service requirement may further include a servicecontinuity requirement.

702. The AMF sends the PDU session modification request message to anSMF.

703. The SMF obtains a PCC rule of the UE in a 5G network and a PCC ruleof the UE in a 4G network by using a PDU-CAN session modificationprocedure.

Optionally, the PCC rules include a QCI of the UE in the 5G network, aQCI of the UE in the 4G network, and at least one of the following:uplink and downlink packet filters (UL+DL Packet filters), a GBR, anMBR, and an ARP. Optionally, the UE may use same uplink and downlinkpacket filters (UL+DL Packet filters), GBR, MBR, and ARP parameters inthe 5G network and the 4G network.

Optionally, the SMF sends a PDU-CAN session modification request messageto a PCF. The PDU-CAN session establishment request message includes theservice requirement of the UE. The PCF generates the PCC rule of the UEin the 5G network and the PCC rule of the UE in the 4G network based onthe service requirement of the UE. The SMF receives a PDU-CAN sessionestablishment response message sent by the PCF. The PDU-CAN sessionestablishment response message includes the PCC rule of the UE in the 5Gnetwork and the PCC rule of the UE in the 4G network.

Optionally, the PCF may further receive a service notification messagesent by an application function (AF) device. The service notificationmessage includes the service requirement of the UE. In this case, thePCF sends a PDU-CAN session modification request message to the SMF. ThePDU-CAN session modification request message includes the PCC rule ofthe UE in the 5G network and the PCC rule of the UE in the 4G network.

704. The SMF sends a dedicated bearer identifier assignment requestmessage to the AMF.

705. The AMF allocates a bearer identifier to a dedicated bearer in aPDN connection corresponding to an APN.

706. The AMF sends a dedicated bearer identifier assignment responsemessage to the SMF, where the dedicated bearer identifier assignmentresponse message includes the bearer identifier that is of the dedicatedbearer and that is allocated by the AMF.

707. The SMF allocates a flow identifier to a dedicated flow in a PDUsession corresponding to a DNN.

In this embodiment, sequences of step 703, step 704 to step 706, andstep 707 may be exchanged. This is not limited herein.

708. The SMF sends a PDU session modification accept message to the AMF,where the PDU session modification accept message includes the flowidentifier that is of the dedicated flow in the PDU sessioncorresponding to the DNN and that is allocated by the SMF.

Optionally, the SMF generates a QoS rule of the UE in the 5G network anda QoS rule of the UE in the 4G network according to the PCC rule of theUE in the 5G network and the PCC rule of the UE in the 4G network.

Optionally, the PDU session modification accept message may furtherinclude session management information. The session managementinformation includes an authorized QoS rule of the dedicated flow in thePDU session and an authorized QoS rule of the dedicated bearer in thePDN connection. Optionally, the authorized QoS rule of the dedicatedflow in the PDU session includes the flow identifier of the dedicatedflow, and the authorized QoS rule of the dedicated bearer in the PDNconnection includes the bearer identifier of the dedicated bearer.

Optionally, the dedicated flow is a GBR flow, and the dedicated beareris a GBR bearer. The authorized QoS rule of the dedicated flow includesan uplink packet filter (UL Packet filter) of the GBR flow, and theauthorized QoS rule of the dedicated bearer includes a traffic flowtemplate (TFT) of the GBR bearer. Optionally, content included in theuplink packet filter is the same as content included in the uplinktraffic flow template herein.

709. The AMF sends a PDU session modification accept message to the UE,where the session modification accept message includes the flowidentifier that is of the dedicated flow and that is allocated by theSMF and the bearer identifier that is of the dedicated bearer and thatis allocated by the AMF.

Optionally, the session modification accept message may further includethe authorized QoS rule of the dedicated flow in the PDU session and theauthorized QoS rule of the dedicated bearer in the PDN connection.

Optionally, a session establishment accept message includes the sessionmanagement information included in the PDU session modification acceptmessage in step 708.

710. The AMF receives a session modification acknowledgement (ACK)message sent by the UE.

711. The AMF sends the session modification acknowledgement message tothe SMF.

712. The SMF sends a session establishment request message to a UPF.

This step is similar to step 606, and details are not described hereinagain.

713. The SMF receives a session establishment response message sent bythe UPF, where the response message includes a tunnel ID of the UPF anda tunnel ID of a PGW-U.

This step is similar to step 607, and details are not described hereinagain.

In this embodiment, in a process in which the UE initiates establishmentof the dedicated flow in the PDU session, the AMF allocates thecorresponding dedicated bearer in the 4G network to the dedicated flowin the session, thereby avoiding a case in which a correspondencebetween the dedicated flow in the PDU session in the 5G network and thededicated bearer in the PDN connection in the 4G network is establishedby using a mapping method. According to the method in this embodiment,interworking of the UE in different networks is simpler. For example,when the UE is handed over from the 5G network to the 4G network, aprocedure is simpler.

FIG. 8 is a further schematic flowchart of a session management methodaccording to an embodiment of this disclosure. In this embodiment, forcontent similar to that in the embodiments of FIG. 2 to FIG. 7, refer todescriptions corresponding to the embodiments of FIG. 2 to FIG. 7, anddetails are not described herein again. Specifically, FIG. 8 showsanother procedure in which UE initiates establishment of a dedicatedflow in a PDU session. A session management method in this embodimentincludes the following steps.

Step 801 to step 803 in this embodiment are similar to step 701 to step703, and details are not described herein again.

804. The SMF allocates a flow identifier to a dedicated flow in a PDUsession corresponding to a DNN.

805. The SMF sends a PDU session modification accept message to the AMF,where the PDU session modification accept message includes the flowidentifier that is of the dedicated flow in the PDU sessioncorresponding to the DNN and that is allocated by the SMF.

Optionally, the SMF generates a QoS rule of the UE in the 5G network anda QoS rule of the UE in the 4G network according to the PCC rule of theUE in the 5G network and the PCC rule of the UE in the 4G network.

Optionally, the PDU session modification accept message may furtherinclude session management information. The session managementinformation includes an authorized QoS rule of the dedicated flow in thePDU session and an authorized QoS rule of a dedicated bearer in a PDNconnection. Optionally, the authorized QoS rule of the dedicated flow inthe PDU session includes the flow identifier of the dedicated flow.

Optionally, the dedicated flow is a GBR flow, and the dedicated beareris a GBR bearer. The authorized QoS rule of the dedicated flow includesan uplink packet filter (UL Packet filter) of the GBR flow, and theauthorized QoS rule of the dedicated bearer includes a traffic flowtemplate (TFT) of the GBR bearer. Optionally, content included in theuplink packet filter is the same as content included in the uplinktraffic flow template herein.

806. The AMF allocates a bearer identifier to a dedicated bearer in aPDN connection corresponding to an APN.

807. The AMF sends a PDU session modification accept message to the UE,where the PDU session modification accept message includes the flowidentifier that is of the dedicated flow and that is allocated by theSMF and the bearer identifier that is of the dedicated bearer and thatis allocated by the AMF.

Optionally, the session modification accept message may further includethe authorized QoS rule of the dedicated flow in the PDU session and theauthorized QoS rule of the dedicated bearer in the PDN connection.

Optionally, a session establishment accept message includes the beareridentifier that is of the dedicated bearer and that is allocated by theAMF and the session management information included in the PDU sessionmodification accept message in step 805.

Step 808 to step 811 in this embodiment are similar to step 710 to step713, and a difference lies in that the PDU session modificationacknowledgement message in step 809 includes the bearer identifier thatis of the dedicated bearer and that is allocated by the AMF.

In this embodiment, in a process in which the UE initiates establishmentof the dedicated flow in the PDU session, the SMF first allocates theflow identifier to the dedicated flow in the PDU session correspondingto the DNN, and then sends the identifier of the dedicated flow to theAMF, so that the dedicated bearer identifier assignment request messageand the dedicated bearer identifier assignment response message in FIG.7 are omitted. Therefore, the procedure is simpler.

In the dedicated flow establishment processes in the embodiments of FIG.7 and FIG. 8, the SMF allocates the flow identifier to the dedicatedflow. This disclosure may further provide an alternative solution: TheSMF aggregates, according to the PCC rule of the UE in the 5G network, aservice data flow corresponding to the PCC rule of the UE in the 5Gnetwork to a dedicated flow established for the UE, and the SMF uses aflow identifier of the dedicated flow established for the UE as anidentifier of a to-be-established dedicated flow. Optionally, the SMFmay determine, based on a QCI and an ARP in the PCC rule, whether toaggregate the service data flow corresponding to the PCC rule to thededicated flow established for the UE. For example, the service dataflow may be aggregated to an established dedicated flow whose QCI andARP are the same as those of the service data flow. Optionally, thealternative solution may be applied to a case in which a quantity ofdedicated flows in a PDU session in the 5G network is greater than aquantity of dedicated bearers in a PDN connection in the 4G network, toavoid a problem that a one-to-one correspondence cannot be establishedbetween the dedicated flows and the dedicated bearers. Certainly, if aone-to-one correspondence can be established between dedicated flows anddedicated bearers, the alternative solution may also be used. This isnot limited herein.

In the dedicated flow establishment processes in the embodiments of FIG.7 and FIG. 8, the AMF allocates the bearer identifier to the dedicatedbearer. This disclosure may further provide an alternative solution: TheSMF aggregates, according to the PCC rule of the UE in the 4G network, aservice data flow corresponding to the PCC rule of the UE in the 4Gnetwork to a dedicated bearer established for the UE, and the SMF uses abearer identifier of the dedicated bearer established for the UE as anidentifier of a dedicated bearer corresponding to the service data flow.Optionally, the SMF may determine, based on a QCI and an ARP in the PCCrule, whether to aggregate the service data flow corresponding to thePCC rule to the dedicated bearer established for the UE. For example,the service data flow may be aggregated to an established dedicatedbearer whose QCI and ARP are the same as those of the service data flow.

FIG. 7 and FIG. 8 show procedures in which the UE initiatesestablishment of the dedicated flow in the PDU session. An embodiment ofthis disclosure further provides a procedure in which a network sideinitiates establishment of a dedicated flow in a PDU session.Specifically, a session management method in this embodiment includes:

A PCF receives a service requirement of UE that is sent by anapplication function network element. The service requirement includesat least one of IP filtering information, a media bandwidth requirementused for QoS control, and an application bandwidth requirement used forQoS control. Optionally, the service requirement may include a servicecontinuity requirement.

The PCF generates a PCC rule of the UE in a 5G network and a PCC rule ofthe UE in a 4G network based on the service requirement of the UE.Optionally, the PCC rules include a QCI of the UE in the 5G network, aQCI of the UE in the 4G network, and at least one of the following:uplink and downlink packet filters, a GBR, an MBR, and an ARP.

The PCF sends a PDU-CAN session modification request message to an SMF.The PDU-CAN session modification request message includes the PCC ruleof the UE in the 5G network and the PCC rule of the UE in the 4Gnetwork.

The following steps in this embodiment are similar to step 704 to step713 or step 804 to step 811, and details are not described herein again.

This disclosure further provides a method for handing over UE betweencommunications networks. FIG. 9 is a schematic flowchart of a method forhanding over UE between communications networks according to anembodiment of this disclosure. The method includes the following steps.

901. UE completes a PDU session and flow establishment process in a 5Gnetwork.

For the process, refer to the session management method and the policyand charging control method that are described above in this disclosure,and details are not described herein.

902. When the UE needs to be handed over from the 5G network to a 4Gnetwork, an access network device in the 5G network sends a handoverrequest to an AMF.

903. The AMF sends a session context request message to an SMF.

904. The AMF receives a session context response message sent by theSMF, where the session context response message includes a beareridentifier and a PCC rule of a default bearer in a PDN connection,and/or a bearer identifier and a PCC rule of a dedicated bearer in a PDNconnection.

905. The AMF sends a relocation request to an MME, where the relocationrequest includes indication information, and the indication informationis used to instruct the MME to reselect an SGW.

Optionally, in the relocation request, address information of the SGWmay be set to 0.0.0.0, to instruct the MME to reselect the SGW.

906. The MME sends a session establishment request message to theselected SGW.

907. The MME receives a session establishment response message sent bythe SGW.

In this embodiment, to ensure handover from the 5G network to the 4Gnetwork, before the handover, the 5G network side reserves sessionmanagement resources for the 4G network; and during the handover, the 5Gnetwork sends the session management resources to the 4G network, andthe 4G network can rapidly set up a service based on the sessionmanagement resources, thereby ensuring service continuity andsimplifying a handover procedure.

FIG. 10 is a schematic block diagram of an access and mobilitymanagement device according to an embodiment of this disclosure. Theaccess and mobility management device includes an obtaining unit 1001,an allocation unit 1002, a receiving unit 1003, and a sending unit 1004.Optionally, the obtaining unit 1001 and the allocation unit 1002 may beprocessors of the access and mobility management device, and thereceiving unit 1003 and the sending unit 1004 may be communicationsinterfaces of the access and mobility management device that areconfigured to receive and transmit information. Specifically, for thereceiving unit 1003 and the sending unit 1004, refer to communicationsinterfaces of the access and mobility management network element in thecommunications architecture shown in FIG. 1.

The obtaining unit 1001 is configured to obtain subscription data of aterminal in a first communications network and subscription data of theterminal in a second communications network. The subscription data ofthe terminal in the first communications network includes a data networkname DNN, and the subscription data of the terminal in the secondcommunications network includes an access point name APN correspondingto the DNN.

Optionally, the subscription data of the terminal in the firstcommunications network further includes a subscription contextcorresponding to the DNN, the subscription data of the terminal in thesecond communications network further includes a PDN subscriptioncontext corresponding to the APN, and a PDU session establishmentrequest message sent by the sending unit to a session management networkelement further includes the subscription context corresponding to theDNN and the PDN subscription context corresponding to the APN.

The allocation unit 1002 is configured to allocate a bearer identifierto a bearer in a PDN connection corresponding to the APN.

The receiving unit 1003 is configured to receive a flow identifier thatis of a flow in a PDU session corresponding to the DNN and that is sentby the session management network element.

The sending unit 1004 is configured to send the bearer identifier andthe flow identifier to the terminal.

The receiving unit 1003 is further configured to: before the allocationunit 1002 allocates the bearer identifier to the bearer in the PDNconnection corresponding to the APN, receive a registration requestmessage or a PDU session establishment request message sent by theterminal. The sending unit is further configured to: after the receivingunit receives the registration request message or the PDU sessionestablishment request message, send the PDU session establishmentrequest message to the session management network element. The bearer inthe PDN connection corresponding to the APN is a default bearer, theflow in the PDU session corresponding to the DNN is a default flow, andthe PDU session establishment request message includes a beareridentifier of the default bearer.

The receiving unit 1003 is further configured to receive a dedicatedbearer identifier assignment request message sent by the sessionmanagement network element, and the sending unit is further configuredto send a dedicated bearer identifier assignment response message to thesession management network element. The bearer in the PDN connectioncorresponding to the APN is a dedicated bearer, the flow in the PDUsession corresponding to the DNN is a dedicated flow, and the dedicatedbearer identifier assignment response message includes a beareridentifier of the dedicated bearer.

The receiving unit 1003 is configured to receive session managementinformation sent by the session management network element. The sessionmanagement information includes an authorized quality of service QoSrule of the flow and an authorized QoS rule of the bearer, theauthorized QoS rule of the flow includes the flow identifier, and theauthorized QoS rule of the bearer includes the bearer identifier.

The sending unit 1004 is further configured to send a location updaterequest message to a subscriber server, and the receiving unit isfurther configured to receive a location update response message sent bythe subscriber server. The location update response message includes thesubscription data of the terminal in the first communications networkand the subscription data of the terminal in the second communicationsnetwork.

The receiving unit 1003 is further configured to receive a handoverrequest sent by an access network device, the sending unit is furtherconfigured to send a session context request message to the sessionmanagement network element, and the receiving unit is further configuredto receive a session context response message sent by the sessionmanagement network element. The session context response messageincludes the bearer identifier and a policy and charging control rule ofthe default bearer in the PDN connection; and/or the bearer identifierand a policy and charging control rule of the dedicated bearer in thePDN connection. The sending unit is further configured to send alocation request to a mobility management entity. The location requestincludes indication information, and the indication information is usedto instruct the mobility management entity to reselect a servinggateway.

The obtaining unit 1001 and the allocation unit 1002 in this embodimentare further configured to implement a data and signal processing-relatedfunction of the access and mobility management device in the embodimentsof FIG. 2 to FIG. 9. The receiving unit 1003 and the sending unit 1004are further configured to implement an information receiving andtransmitting-related function of the access and mobility managementnetwork element in the embodiments of FIG. 2 to FIG. 9.

FIG. 11 is a schematic block diagram of a session management deviceaccording to an embodiment of this disclosure. The session managementdevice includes an obtaining unit 1101, a sending unit 1102, and areceiving unit 1103. Optionally, the obtaining unit 1101 may be aprocessor of the session management device, and the sending unit 1102and the receiving unit 1103 may be communications interfaces of thesession management device that are configured to receive and transmitinformation. Specifically, for the sending unit 1102 and the receivingunit 1103, refer to communications interfaces of the session managementnetwork element in the communications architecture shown in FIG. 1.

The obtaining unit 1101 is configured to: obtain a flow identifier of aflow in a PDU session corresponding to a DNN of a terminal, and obtain abearer identifier of a bearer in a PDN connection corresponding to anAPN of the terminal. The DNN is a DNN in subscription data of theterminal in a first communications network, and the APN is an APN insubscription data of the terminal in a second communications network.

The sending unit 1102 is configured to send the bearer identifier andthe flow identifier to an access and mobility management networkelement.

The receiving unit 1103 is configured to receive a PDU sessionestablishment request message sent by the access and mobility managementnetwork element. The bearer in the PDN connection corresponding to theAPN is a default bearer, the flow in the PDU session corresponding tothe DNN is a default flow, and the PDU session establishment requestmessage includes the bearer identifier.

Optionally, the subscription data of the terminal in the firstcommunications network further includes a subscription contextcorresponding to the DNN, the subscription data of the terminal in thesecond communications network further includes a PDN subscriptioncontext corresponding to the APN, and the PDU session establishmentrequest message further includes the subscription context correspondingto the DNN and the PDN subscription context corresponding to the APN.

Optionally, the sending unit 1102 is further configured to send aPDU-CAN session establishment request message to a policy and chargingnetwork element. The PDU-CAN session establishment request messageincludes the subscription context corresponding to the DNN and the PDNsubscription context corresponding to the APN. The receiving unit isfurther configured to receive a PDU-CAN session establishment responsemessage sent by the policy and charging network element. The PDU-CANsession establishment response message includes a policy and chargingcontrol PCC rule of the terminal in the first communications network anda policy and charging control PCC rule of the terminal in the secondcommunications network.

Optionally, the sending unit 1102 is further configured to send adedicated bearer identifier assignment request message to the access andmobility management network element, and the receiving unit isconfigured to receive a dedicated bearer identifier assignment responsemessage sent by the access and mobility management network element. Thebearer in the PDN connection corresponding to the APN is a dedicatedbearer, the flow in the PDU session corresponding to the DNN is adedicated flow, and the dedicated bearer identifier assignment responsemessage includes a bearer identifier of the dedicated bearer.

Optionally, the receiving unit 1103 is further configured to receive aPDU-CAN session modification request message sent by a policy andcharging network element. The PDU-CAN session modification requestmessage includes a PCC rule of the terminal in the first communicationsnetwork and a PCC rule of the terminal in the second communicationsnetwork.

Optionally, the sending unit 1103 is configured to send sessionmanagement information to the access and mobility management networkelement. The session management information includes an authorized QoSrule of the flow and an authorized QoS rule of the bearer, theauthorized QoS rule of the flow includes the flow identifier, and theauthorized QoS rule of the bearer includes the bearer identifier.

Optionally, the obtaining unit 1101 is configured to aggregate,according to the PCC rule of the terminal in the first communicationsnetwork, a service data flow corresponding to the PCC rule of theterminal in the first communications network to a dedicated flowestablished for the terminal. A flow identifier that is of the dedicatedflow and that is obtained by the session management network element is aflow identifier of the dedicated flow established for the terminal.

Optionally, the obtaining unit is configured to aggregate, according tothe PCC rule of the terminal in the second communications network, aservice data flow corresponding to the PCC rule of the terminal in thesecond communications network to a dedicated bearer established for theterminal. The bearer identifier that is of the dedicated bearer and thatis obtained by the session management network element is a beareridentifier of the dedicated bearer established for the terminal.

The obtaining unit 1101 in this embodiment is further configured toimplement a data and signal processing-related function of the sessionmanagement network element in the embodiments of FIG. 2 to FIG. 9. Thesending unit 1102 and the receiving unit 1103 are further configured toimplement an information receiving and transmitting-related function ofthe session management network element in the embodiments of FIG. 2 toFIG. 9.

FIG. 12 is a schematic structural diagram of a policy and chargingcontrol device according to an embodiment of this disclosure. The policyand charging control device includes an obtaining unit 1201, a sendingunit 1202, and a receiving unit 1203. Optionally, the obtaining unit1201 may be a processor of the policy and charging control device, andthe sending unit 1202 and the receiving unit 1203 may be communicationsinterfaces of the policy and charging control device that are configuredto receive and transmit information. Specifically, for the sending unit1202 and the receiving unit 1203, refer to communications interfaces ofthe policy and charging network element in the communicationsarchitecture shown in FIG. 1.

The obtaining unit 1201 is configured to obtain a service requirement ofa terminal.

The sending unit 1202 is configured to send a PDU-CAN session managementmessage to a session management network element. The PDU-CAN sessionmanagement message includes a policy and charging control PCC rule ofthe terminal in a first communications network and a policy and chargingcontrol PCC rule of the terminal in a second communications network.

The receiving unit 1203 is configured to receive a PDU-CAN sessionestablishment request message sent by the session management networkelement. The PDU-CAN session establishment request message includes asubscription context corresponding to a DNN of the terminal in the firstcommunications network and a PDN subscription context corresponding toan APN of the terminal in the second communications network.

Optionally, the PCC rule of the terminal in the first communicationsnetwork and the PCC rule of the terminal in the second communicationsnetwork include: a quality of service class identifier of the terminalin the first communications network, an authorized Session-AMBR of adefault flow in a PDU session corresponding to the DNN, a quality ofservice class identifier of the terminal in the second communicationsnetwork, and an authorized APN-AMBR of a default bearer in a PDNconnection corresponding to the APN.

Optionally, the receiving unit 1203 is configured to receive the servicerequirement sent by the terminal or an application function networkelement. The service requirement includes at least one of InternetProtocol IP filtering information, a media bandwidth requirement usedfor quality of service QoS control, and an application bandwidthrequirement used for quality of service QoS control.

Optionally, the PCC rule of the terminal in the first communicationsnetwork and the PCC rule of the terminal in the second communicationsnetwork include: a quality of service class identifier of the terminalin the first communications network, a quality of service classidentifier of the terminal in the second communications network, and atleast one of the following: uplink and downlink packet filters, aguaranteed bit rate GBR, a maximum bit rate MBR, and an allocation andretention priority ARP. Optionally, the service requirement furtherincludes a service continuity requirement.

The obtaining unit 1201 in this embodiment is further configured toimplement a data and signal processing-related function of the policyand charging control network element in the embodiments of FIG. 2 toFIG. 9. The sending unit 1202 and the receiving unit 1203 are furtherconfigured to implement an information receiving andtransmitting-related function of the policy and charging network elementin the embodiments of FIG. 2 to FIG. 9.

FIG. 13 is another schematic structural diagram of an access andmobility management device according to an embodiment of thisdisclosure. The access and mobility management device includes aprocessor 1301, a memory 1302, and a communications interface 1303. Theprocessor 1301, the memory 1302, and the communications interface 1303may be connected to each other by using a bus 1304. The bus 1304 may bea peripheral component interconnect (PCI) bus, an extended industrystandard architecture (EISA) bus, or the like. The bus 404 may includean address bus, a data bus, a control bus, and the like.

Although FIG. 13 shows only one communications interface 1303, there mayalternatively be a plurality of communications interfaces 1303. Forexample, in the communications architecture shown in FIG. 1, thecommunications interface may include an N2 interface, an Nx interface,an N11 interface, an N15 interface, and an N18 interface. The access andmobility management device (such as an AMF) is connected to another corenetwork device by using a corresponding interface, and receives andtransmits information by using a corresponding interface.

The processor 1301 may be a central processing unit (CPU), a networkprocessor (NP), or a combination of the CPU and the NP. The processormay further include a hardware chip. The hardware chip may be anapplication-specific integrated circuit (ASIC), a programmable logicdevice (PLD), or a combination thereof. The PLD may be a complexprogrammable logical device (CPLD), a field-programmable gate array(FPGA), a generic array logic (GAL), or a combination thereof. AlthoughFIG. 13 shows only one processor 1301, there may alternatively be aplurality of processors 1301 or processing units.

The memory may be a volatile memory or a non-volatile memory, or mayinclude a volatile memory and a non-volatile memory. The non-volatilememory may be a read-only memory (ROM), a programmable read-only memory(PROM), an erasable programmable read-only memory (EPROM), anelectrically erasable programmable read-only memory (EEPROM), or a flashmemory. The volatile memory may be a random access memory (RAM), and isused as an external cache. In FIG. 13, the memory 1302 may alternativelybe a storage unit in the processor 1301.

An instruction stored in the memory 1302 may make the processor 1301perform the following operations: obtaining subscription data of aterminal in a first communications network and subscription data of theterminal in a second communications network by using the communicationsinterface 1303, where the subscription data of the terminal in the firstcommunications network includes a DNN, and the subscription data of theterminal in the second communications network includes an APNcorresponding to the DNN; allocating a bearer identifier to a bearer ina PDN connection corresponding to the APN; receiving, by using thecommunications interface 1303, a flow identifier that is of a flow in aPDU session corresponding to the DNN and that is sent by a sessionmanagement network element; and sending, by using the communicationsinterface 1303, the bearer identifier and the flow identifier to theterminal.

The processor in this embodiment is further configured to: implement adata and signal processing-related function of the access and mobilitymanagement device in the embodiments of FIG. 2 to FIG. 9, and perform acorresponding data and signal processing step. The communicationsinterface 1303 is further configured to: implement an informationreceiving and transmitting-related function of the access and mobilitymanagement network element in the embodiments of FIG. 2 to FIG. 9, andperform a corresponding information receiving and transmitting step.

An embodiment of this disclosure further provides another sessionmanagement device. The session management device has a structure similarto that of the access and mobility management device in FIG. 13.However, a communications interface may include an N4 interface, an N7interface, an N11 interface, and an N10 interface in the communicationsarchitecture shown in FIG. 1. The session management device (such as anSMF) is connected to another core network device by using acorresponding interface, and receives and transmits information by usinga corresponding interface.

Correspondingly, an instruction stored in a memory of the sessionmanagement device may make the processor perform the followingoperations: obtaining a flow identifier of a flow in a PDU sessioncorresponding to a DNN of a terminal, where the DNN is a DNN insubscription data of the terminal in a first communications network;obtaining a bearer identifier of a bearer in a PDN connectioncorresponding to an APN of the terminal, where the APN is an APN insubscription data of the terminal in a second communications network;and sending the bearer identifier and the flow identifier to an accessand mobility management network element by using the communicationsinterface.

The processor in this embodiment is further configured to: implement adata and signal processing-related function of the session managementnetwork element in the embodiments of FIG. 2 to FIG. 9, and perform acorresponding data and signal processing step. The communicationsinterface is further configured to: implement an information receivingand transmitting-related function of the session management networkelement in the embodiments of FIG. 2 to FIG. 9, and perform acorresponding information receiving and transmitting step.

An embodiment of this disclosure further provides another policy andcharging control device. The policy and charging control device has astructure similar to that of the access and mobility management devicein FIG. 13. However, a communications interface may include an N7interface and an N15 interface in the communications architecture shownin FIG. 1. The policy and charging control device (such as a PCR) isconnected to another core network device by using a correspondinginterface, and receives and transmits information by using acorresponding interface.

Correspondingly, an instruction stored in a memory of the policy andcharging control device may make the processor perform the followingoperations: obtaining a service requirement of a terminal; and sending aPDU-CAN session management message to a session management networkelement by using the communications interface, where the PDU-CAN sessionmanagement message includes a policy and charging control PCC rule ofthe terminal in a first communications network and a policy and chargingcontrol PCC rule of the terminal in a second communications network.

The processor in this embodiment is further configured to: implement adata and signal processing-related function of the policy and chargingcontrol device in the embodiments of FIG. 2 to FIG. 9, and perform acorresponding data and signal processing step. The communicationsinterface is further configured to: implement an information receivingand transmitting-related function of the policy and charging controldevice in the embodiments of FIG. 2 to FIG. 9, and perform acorresponding information receiving and transmitting step.

An embodiment of the present invention further provides a computerstorage medium or a computer program product, configured to store aninstruction that can be executed by a processor and that is stored inthe foregoing memory.

All or some of the foregoing embodiments may be implemented by usingsoftware, hardware, firmware, or any combination thereof. When theembodiments are implemented by using the software, all or some of theembodiments may be implemented in a form of a computer program product.The computer program product may include one or more computerinstructions. When the computer program instruction is loaded andexecuted on a computer, all or some of the procedures or functionsaccording to the embodiments of this disclosure are generated. Thecomputer may be a general-purpose computer, a dedicated computer, acomputer network, or another programmable apparatus. The computerinstruction may be stored in a computer-readable storage medium or maybe transmitted from a computer-readable storage medium to anothercomputer-readable storage medium. For example, the computer instructionmay be transmitted from a website, computer, server, or data center toanother website, computer, server, or data center in a wired (forexample, a coaxial cable, an optical fiber, or a digital subscriber line(DSL)) or wireless (for example, infrared, radio, or microwave) manner.The computer-readable storage medium may be any usable medium accessibleby a computer, or a data storage device such as a server or a datacenter that integrates one or more usable media. The usable medium maybe a magnetic medium (such as a soft disk, a hard disk, or a magneticdisk), an optical medium (such as a DVD), a semiconductor medium (suchas a solid state disk Solid State Disk (SSD)), or the like.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented by usingelectronic hardware or a combination of computer software and theelectronic hardware. Whether the functions are performed by usinghardware or software depends on particular applications and designconstraint conditions of the technical solutions. A person skilled inthe art may use different methods to implement the described functionsfor each particular application, but it should not be considered thatthe implementation goes beyond the scope of this disclosure.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, refer to acorresponding process in the foregoing method embodiments, and detailsare not described herein again.

In the several embodiments provided in this disclosure, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiment is merely an example. For example, the unit division ismerely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected according toactual requirements to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of this disclosure maybe integrated into one processing unit, or each of the units may existalone physically, or two or more units are integrated into one unit.

When the functions are implemented in the form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer-readable storage medium. Based on such anunderstanding, the technical solutions of this disclosure essentially,or the part contributing to the prior art, or some of the technicalsolutions may be implemented in a form of a software product. Thesoftware product is stored in a storage medium, and includes severalinstructions for instructing a computer device (which may be a personalcomputer, a server, or a network device) to perform all or some of thesteps of the methods described in the embodiments of this disclosure.The foregoing storage medium includes any medium that can store programcode, such as a USB drive, a removable hard disk, a read-only memory, arandom access memory, a magnetic disk, or an optical disc.

The foregoing descriptions are merely specific implementations of thisdisclosure, but are not intended to limit the protection scope of thisdisclosure. Any variation or replacement readily figured out by a personskilled in the art within the technical scope disclosed in thisdisclosure shall fall within the protection scope of this disclosure.Therefore, the protection scope of this disclosure shall be subject tothe protection scope of the claims.

1. A method for allocating bearer identifier, comprising: receiving, byan access and mobility management network element in a firstcommunication network, a bearer identifier assignment request messagefrom a session management network element in the first communicationnetwork in a procedure for establishing a dedicated flow in a packetdata unit (PDU) session in the first communication network; allocating,by the access and mobility management network element, the beareridentifier to a dedicated bearer in a second communication network, thededicated bearer in the second communication network corresponding tothe dedicated flow in the first communication network, the firstcommunication network is a 5G communication network and the secondcommunication network is a 4.5G or 4G communication network; andsending, by the access and mobility management network element, a beareridentifier assignment response message to the session management networkelement, the bearer identifier assignment response message comprisingthe bearer identifier.
 2. The method according to claim 1, furthercomprising: receiving, by the access and mobility management networkelement, a handover request from an access network device in the firstcommunications network, wherein the handover request requests tohandover a terminal from the first communications network to the secondcommunications network; sending, by the access and mobility managementnetwork element, a session context request message to the sessionmanagement network element; and receiving, by the access and mobilitymanagement network element, a session context response message from thesession management network element, the session context response messagecomprising the bearer identifier.
 3. The method according to claim 2,further comprising: sending, by the access and mobility managementnetwork element, a relocation request to a mobility management entity inthe second communications network, the relocation request comprisingindication information instructing the mobility management entity toreselect a serving gateway in second communications network.
 4. Themethod according to claim 3, wherein the indication information isaddress information of a serving gateway.
 5. The method according toclaim 1, further comprising: receiving, by the access and mobilitymanagement network element, a registration request message from aterminal, the registration request message comprising indicationinformation indicating that the terminal has a capability to performcommunication in the first communications network and in the secondcommunications network.
 6. The method according to claim 1, wherein theprocedure for establishing the dedicated flow in the PDU session in thefirst communication network, comprises: a terminal initiated procedurefor establishing the dedicated flow in the PDU session in the firstcommunication network, or a network side initiated procedure forestablishing the dedicated flow in the PDU session in the firstcommunication network.
 7. The method according to claim 1, whereinbefore receiving, by the access and mobility management network element,the bearer identifier assignment request message, the method furthercomprises: receiving, by the access and mobility management networkelement, a PDU session modification request message from a terminal; andsending, by the access and mobility management network element, a PDUsession modification request message to the session management networkelement.
 8. The method according to claim 7, wherein after sending, bythe access and mobility management network element, the beareridentifier assignment response message to the session management networkelement, the method further comprises: receiving, by the access andmobility management network element, a PDU session modification acceptmessage from the session management network element, wherein the PDUsession modification accept message comprises the bearer identifier anda flow identifier allocated by the session management network element tothe dedicated flow.
 9. The method according to claim 8, wherein the PDUsession modification accept message further comprises quality of service(QoS) parameters corresponding to the dedicated flow and QoS parameterscorresponding to the dedicated bearer.
 10. The method according to claim8, further comprising: sending, by the access and mobility managementnetwork element, a PDU session modification accept message to theterminal, the PDU session modification accept message comprising thebearer identifier and the flow identifier.
 11. A communication method,comprising: receiving, by an access and mobility management networkelement in a first communication network, a bearer identifier assignmentrequest message from a session management network element in the firstcommunication network in a procedure for establishing a dedicated flowin a packet data unit (PDU) session in the first communication network;allocating, by the access and mobility management network element, abearer identifier to a dedicated bearer in a second communicationnetwork, the dedicated bearer in the second communication networkcorresponding to the dedicated flow in the first communication network,the first communication network is a 5G communication network and thesecond communication network is a 4.5G or 4G communication network;sending, by the access and mobility management network element, a beareridentifier assignment response message to the session management networkelement, the bearer identifier assignment response message comprisingthe bearer identifier; allocating, by the session management networkelement, a flow identifier to the dedicated flow; and sending, by thesession management network element through the access and mobilitymanagement network element, the bearer identifier and the flowidentifier to a terminal.
 12. An apparatus, comprising: a memory storinginstructions; and at least one processor coupled with the memory, the atleast one processor executing the instructions to perform the followingsteps: receiving a bearer identifier assignment request message from asession management network element in a first communication network in aprocedure for establishing a dedicated flow in a packet data unit (PDU)session in the first communication network; allocating a beareridentifier to a dedicated bearer in a second communication network, thededicated bearer in the second communication network corresponding tothe dedicated flow in the first communication network, the firstcommunication network is a 5G communication network and the secondcommunication network is a 4.5G or 4G communication network; and sendinga bearer identifier assignment response message to the sessionmanagement network element, the bearer identifier assignment responsemessage comprising the bearer identifier.
 13. The apparatus according toclaim 12, wherein the at least one processor is further configured toexecute the instructions to further perform the following steps:receiving a handover request from an access network device in the firstcommunications network, wherein the handover request requests tohandover a terminal from the first communications network to the secondcommunications network; sending a session context request message to thesession management network element; and receiving a session contextresponse message from the session management network element, thesession context response message comprising the bearer identifier. 14.The apparatus according to claim 13, wherein the at least one processoris further configured to execute the instructions to further perform thefollowing step: sending a relocation request to a mobility managemententity in the second communications network, the relocation requestcomprising indication information instructing the mobility managemententity to reselect a serving gateway in second communications network.15. The apparatus according to claim 12, wherein the procedure forestablishing the dedicated flow in the PDU session in the firstcommunication network comprises: a terminal initiated procedure forestablishing the dedicated flow in the PDU session in the firstcommunication network, or a network side initiated procedure forestablishing the dedicated flow in the PDU session in the firstcommunication network.
 16. The apparatus according to claim 12, whereinthe at least one processor is further configured to execute theinstructions to further perform the following steps: receiving a PDUsession modification request message from a terminal before receivingthe bearer identifier assignment request message; and sending a PDUsession modification request message to the session management networkelement.
 17. The apparatus according to claim 16, wherein the at leastone processor is further configured to execute the instructions tofurther perform the following step: receiving a PDU session modificationaccept message from the session management network element after sendingthe bearer identifier assignment response message to the sessionmanagement network element, wherein the PDU session modification acceptmessage comprises the bearer identifier and a flow identifier allocatedby the session management network element to the dedicated flow.
 18. Theapparatus according to claim 17, wherein the PDU session modificationaccept message further comprises quality of service (QoS) parameterscorresponding to the dedicated flow and QoS parameters corresponding tothe dedicated bearer.
 19. The apparatus according to claim 17, whereinthe at least one processor is further configured to execute theinstructions to further perform the following step: sending a PDUsession modification accept message to the terminal, the PDU sessionmodification accept message comprising the bearer identifier and theflow identifier.
 20. A first communication system, comprising: an accessand mobility management network element; and a session managementnetwork element in communication with the access and mobility managementnetwork element; the access and mobility management network element isconfigured to: receive a bearer identifier assignment request messagefrom the session management network element in a procedure forestablishing a dedicated flow in a packet data unit (PDU) session in thefirst communication system; allocate a bearer identifier to a dedicatedbearer in a second communication system; and send a bearer identifierassignment response message to the session management network element,the dedicated bearer in the second communication system corresponding tothe dedicated flow in the first communication system, the firstcommunication system is a 5G communication network and the secondcommunication system is a 4.5G or 4G communication system, the beareridentifier assignment response message comprises the bearer identifier;and the session management network element is configured to: allocate aflow identifier to the dedicated flow; and send the bearer identifierand the flow identifier to a terminal through the access and mobilitymanagement network element.